Enlarged substrate for magnetic recording medium

ABSTRACT

An enlarged substrate for a magnetic recording medium used in a data storage device such as a hard disc drive (HDD). In some embodiments, an apparatus includes a substrate for a magnetic recording disc for installation in a 3½ inch form factor hard disc drive, the substrate having an overall diameter of nominally from 96.9 mm to 100.4 mm. In other embodiments, an apparatus comprises a substrate for a magnetic recording disc for installation in a 2½ inch form factor hard disc drive, the substrate having an overall diameter of nominally from 66.9 mm to 71.8 mm. In other embodiments, a data storage device has a magnetic recording medium that uses an enlarged substrate as set forth above.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/552,189 filed Nov. 24, 2014 which is a continuation of U.S.Pat. No. 8,896,964 issued on Nov. 25, 2014 (formerly Ser. No. 14/044,621filed Oct. 2, 2013) which makes a claim of domestic priority under 35U.S.C. §119(e) to U.S. Provisional Application No. 61/824,271 filed May16, 2013, the contents of which are incorporated by reference.

SUMMARY

Various embodiments of the present disclosure are generally directed toan enlarged substrate for a magnetic recording medium used in a datastorage device such as a hard disc drive (HDD).

In some embodiments, an apparatus includes a substrate for a magneticrecording disc for installation in a 3½ inch form factor hard discdrive, the substrate having an overall diameter of nominally from 96.9mm to 100.4 mm. In other embodiments, an apparatus comprises a substratefor a magnetic recording disc for installation in a 2½ inch form factorhard disc drive, the substrate having an overall diameter of nominallyfrom 66.9 mm to 71.8 mm. In other embodiments, a data storage device hasa magnetic recording medium that uses an enlarged substrate as set forthabove.

These and other features of various embodiments can be understood from areview of the following detailed description in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged substrate for use in a 3½ inch form factor harddisc drive (HDD) in accordance with some embodiments.

FIG. 2 is an enlarged substrate for use in a 2½ inch form factor HDD inaccordance with some embodiments.

FIG. 3 is a cross-sectional, elevational view of another enlargedsubstrate that may correspond to the substrates of FIGS. 1-2.

FIG. 4 is an end view of another enlarged substrate with a duboff (DO)zone.

FIG. 5 is an end view of another enlarged substrate with a ski jump (SJ)zone.

FIG. 6 is a schematic representation of different sized substratessharing a common DO profile.

FIG. 7 is a schematic representation of different sized substratessharing a common SJ profile.

FIG. 8 is a schematic representation of different sized substrates withdifferent DO profiles.

FIG. 9 is a schematic representation of different sized substrates withdifferent SJ profiles.

FIG. 10 is a top plan view of a polishing assembly adapted to polishenlarged substrates as in FIGS. 1-9 in accordance with some embodiments.

FIG. 11 illustrates a carrier used in FIG. 10.

FIG. 12 is a cross-sectional, elevational view of the polishing systemin FIG. 10.

FIG. 13 is a schematic representation of a magnetic recording mediumformed using the enlarged substrates of FIGS. 1-9 in accordance withsome embodiments.

FIG. 14 is an exploded representation of a hard disc drive (HDD) thatuses the recording medium of FIG. 13 in accordance with someembodiments.

FIG. 15 illustrates a sidewall of a base deck housing member of an HDDsuch as represented in FIG. 14 in accordance with some embodiments.

FIG. 16 is another sidewall of a base deck housing member in accordancewith some embodiments.

FIG. 17 is a side elevational representation of the base deck housingmember of FIG. 16.

FIG. 18 shows the base deck housing member of FIG. 16 with an attachedcover member.

FIG. 19 is a schematic representation of another data storage devicethat uses a magnetic recording medium having an enlarged substrate.

FIG. 20 is a schematic representation of another data storage devicethat uses a magnetic recording medium having an enlarged substrate.

FIG. 21 illustrates a format for a track on a magnetic recording mediumhaving an enlarged substrate.

DETAILED DESCRIPTION

The present disclosure is generally directed to an enlarged substrateconfiguration for magnetic recording media. Magnetic recording media areoften provided in the form of rotatable magnetic recording discs whichare incorporated into a hard disc drive (HDD) data storage device. Thediscs are rotated at a selected rotational velocity and accessed by amoveable read/write transducing head (“transducer”) which records andreads data in the form of magnetic domains.

The progression in the HDD industry from 14 inch, 11 inch, 8 inch, 5½inch, 3½ inch, 2½ inch to 1.8 inch and smaller storage device formfactors is well documented. The progression to successively smaller formfactor sizes was initiated by the floppy disk market, and followed byHDD manufacturers which produced HDDs of corresponding size. This was inpart due to the standardization of mounting sizes of computer bays thatcould be used to secure the respective floppy disk drives and hard discdrives.

Each smaller form factor was (and remains) generally half as wide andhalf as long as the immediately larger form factor. This essentiallyallows two smaller devices to fit in the space provided for one largerdevice. For example, a 3½ inch form factor HDD has length and widthdimensions of nominally 146.1 millimeters, mm (5.75 inches, in) by 101mm (4.00 in). A 2½ inch form factor HDD has length and width dimensionsof nominally 101 mm (4.00 in) by 73 mm (2.88 in), and so on.

Some of the earliest versions of commercially successful hard discdrives were referred to as “Winchester” drives, based on the so-called30/30 system configuration from International Business Machines (IBM).The smaller 8 inch and 5½ inch versions were also referred to as“Winchester” drives. Smaller form factor drives in what later becameknown as the 3½ inch form factor class were initially widely referred toas “Micro-Winchester” drives. The 2½ inch drives did not enjoy a commonmoniker but were sometimes referred to as either“Micro-Miniature-Winchester” or “Mini-Winchester” drives. The HDDindustry quickly standardized on a media size of 95 mm (OD) discs forthe 3½ inch form factor and 65 mm (OD) discs for the 2½ inch formfactor.

A typical magnetic recording disc comprises a magnetic recordingstructure that is formed on an underlying substrate. The recordingstructure can take a variety of forms and may include seed layers,interlayers, a soft underlayer, one or more magnetic recording layers, acarbon overcoat (COC) layer, a lubricant layer, etc. The substrate canbe formed from a suitable rigid, disc-shaped material such as glass,metal, etc.

For magnetic recording discs that are incorporated into 2½ inch formfactor and 3½ inch form factor HDDs, the substrates normally include aninner sidewall at a radius of 12.5 mm, an outer sidewall at a radius ofnominally 32.5 mm (for 65 mm discs) and 47.5 mm (for 95 mm discs),opposing top and bottom flat surfaces that extend substantially from theinner sidewall to the outer sidewall, and relatively small, inner andouter chamfered surfaces between the top and bottom flat surfaces andthe respective inner and outer sidewalls. The chamfered surfaces extendat a suitable angle, such as 45 degrees, and provide gripping surfacesfor use during manufacturing since it is generally undesirable tomechanically contact either the flat surfaces of the substrates or theflat surfaces of the completed magnetic recording media. Substratethicknesses can vary but may be on the order of around 1 mm.

A polishing process is often applied to a substrate prior to theformation of the recording structure thereon. The polishing process isintended to achieve a specified flatness for the top and bottom flatsurfaces of the substrate in terms of maximum axial deviation inlocalized changes in elevation of the substrate material.

One difficulty associated with the substrate polishing process relatesto relief zones that tend to be formed adjacent the respective inner andouter ends of the flat surfaces. The sharp junctions between the flatsurfaces and the respective inner and outer chamfered surfaces tend tobe treated as high points by the polishing process, so that abruptrelief zones may be formed on the substrate adjacent the inner and outersidewalls.

The relief zones can provide negative deviation or positive deviationfrom the elevation of the adjacent flat surface. Negative deviationrelief zones are sometimes referred to as duboff (DO) zones, andpositive deviation relief zones are sometimes referred to as ski jump(SJ) zones. The relief zones can extend a significant radial distanceacross the surfaces of the substrates, such as on the order of about 2mm.

The relief zones located adjacent the inner sidewall of a substrate maynot have a significant effect on performance since this portion of thefinished recording disc is usually covered by an inner clamp or spacerring used to secure the finished disc to a spindle motor hub. The reliefzone located adjacent the outer sidewall, however, can have asignificant effect on overall HDD performance. The outermost active areaof a magnetic recording disc has the highest linear velocity in aconstant angular velocity, CAV rotation system, and accordingly providesthe highest available data transfer rate. The outermost active area thusrepresents the most valuable real estate on the entire disc and is oftenutilized for high speed caching and other data I/O intensive storageapplications.

Data transducers are designed to be hydrodynamically supported (e.g.,“fly”) in very close proximity and in non-contacting relation with theassociated recording surfaces of a magnetic recording medium. Suchtransducers can provide stable and controllable flight over areas havingflatness within a very small tolerance, such as +/−5 nanometers, nm(10⁻⁹ m).

As a data transducer is moved outwardly over a relief zone that changesin elevation away from the flat recording area of a disc, such as bycurving down in a DO zone or curving upwardly in an SJ zone, at somepoint the flight characteristics of the data transducer will becomeunstable and the transducer will experience a variety of undesiredflight characteristics including increased fly height, oscillationsand/or disc contact. In some cases it has been found that datatransducers become unstable responsive to a positive or negative changein elevation over a range beginning as little as about 100-200 nm. Asfly heights and transducing element sizes continue to decrease, it isexpected that sensitivity to elevational changes in the disc topographywill continue to increase, so that future heads will become unstable ateven lower elevational ranges.

The substrate polishing process involves a tradeoff between achievingspecified flatness requirements over the majority of the recordingsurface area and obtaining well controlled relief zone characteristics.Enhancements to the polishing of the flat areas of a substrate can, insome cases, degrade the characteristics of the substrate near theoutermost diameter of the substrate, and vice versa. More specifically,polishing parameters such as pad compressibility, abrasive particlesize, applied polishing force, duration, slurry composition, etc. can beoptimized to obtain a smoother (flatter) surface, but this is often atthe expense of greater erosion/deformation in the outer relief zone,which can effect the ultimate radius at which data can be reliablywritten on a finished recordable medium. Conversely, tuning a polishingprocess to achieve desired outer relief zone characteristics can resultin less than desired levels of flatness of the main flat extents of thesubstrate.

Accordingly, various embodiments of the present disclosure are generallydirected to a novel approach whereby a larger zone of substrate flatnessis achieved for existing form factor HDD products through the use ofenlarged substrates. As explained below, in some embodiments an enhancedsubstrate size is used for a given HDD form factor size. For purposes ofillustration and not by way of limitation, in some cases substrateshaving an outer diameter of nominally 97 mm, rather than the standard 95mm, are used to form media for a 3½ inch form factor HDD. Similarly,substrates having an outer diameter of nominally 67 mm, rather than thestandard 65 mm, are used to form media for a 2½ inch form factor HDD.

Other enhanced sizes can be used. For example, in some cases, substratesof nominally 98 mm and 68 mm are used. In other cases, substrates ofnominally 99 and 69 mm are used. In still other cases, substrates offrom about 96.9 mm up to about 100.4 mm are used for 3½ inch form factordrives, and substrates of from about 66.9 mm up to about 71.8 mm areused for 2½ inch form factor drives. In still further cases, substratesgreater than 100.4 mm are used in 3½ in form factor drives andsubstrates greater than 71.8 mm are used in 2½ inch form factor drives.

The use of substrates of at least about 97 mm and 67 mm in diameter,respectively, provides at least an additional 1 mm of radial distanceoutwardly for each substrate as compared to the standard substrate sizesof 95 mm and 65 mm. Such sizes of substrates, and finished recordingmedia, can be readily accommodated in the associated form factor sizes;more specifically, a nominally 97 mm disc can readily be accommodatedinto a 3½ inch form factor HDD with nominal dimensions of about 146.1 mmby about 101 mm, and a nominally 67 mm disc can readily be accommodatedinto a 2½ inch form factor HDD with nominal dimensions of about 101 mmby about 73 mm.

In some embodiments, the same polishing parameters are utilized topolish the respective 97 mm and 67 mm OD media as is used for respective95 mm and 65 mm OD media. It will be appreciated that, all thingsotherwise being equal, a 97 mm OD substrate will have generally the sameDO and/or ski jump elevation zone characteristics as a 95 mm ODsubstrate subjected to the same processing, and the same is generallytrue for a 67 mm OD substrate as compared to a 65 mm OD substrate. Theradial location of the associated outer relief zones, however, will bemoved outwardly by about 1 mm or more.

While not necessarily required, derating the radial distance dedicatedto the storage of data in an HDD, so that less than the extra 1 mm ofradial distance is actually used to record data, can producesignificantly better manufacturing yields and product performance. Insome embodiments, a derating factor X which is less than 1 is applied,such as an X factor of 0.70. In other embodiments, derating factorsinclude but are not limited to 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30,0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.75, 0.80, 0.85, 0.90, 0.95,0.96, 0.97, 0.98 or 0.99. Other derating values can be used as well.

In this way, less than the entire extra amount of space is used torecord data; for example, if nominally 1 extra mm of radial extent isprovided, then a derating factor of 0.70 results in an 0.70 mm ofadditional recording area, which is located at the most valuablelocation on the disc. It will be appreciated that other derating factorscan be used, including derating factors that are less than or greaterthan 0.70. In some cases, a derating factor of 0 is used so that thelarger disc has the same data storage area as a conventionally sizeddisc (e.g., a 97 mm disc stores the same amount of data as a 95 mm disc;a 67 mm disc stores the same amount of data as a 65 mm disc). In othercases, a derating factor of 0.99 is used so that almost all of the newlyavailable area is used for the recording of data.

These and other features of various embodiments of the presentdisclosure can be understood beginning with a review of FIG. 1 whichprovides a top plan view of an example substrate 100. The substrate 100is formed of glass, and may be subjected to chemical processing as isknown in the art. Other material configurations and processing can beused, including substrates made of aluminum or other metals, etc. Thesubstrate 100 has an overall diameter D, which in this case is nominally97 mm, and is designed for recording media to be used in a hard discdrive (HDD) of 3½ inch form factor. Other sizes can be used, includingbut not limited to an outermost diameter of nominally 98 mm.

The substrate 100 has a center point 102 about which the substrate (andfinished medium) is configured to rotate. An inner sidewall 104 forms acentral aperture in the substrate 100. The sidewall is provided at aselected radius such as nominally 12.5 mm from the center point 102. Thesubstrate has an outer sidewall 106, which constitutes a substantiallyvertically extending edge, at a radius of nominally 48.5 mm from thecenter point 102. It will be appreciated that other diameters for thesubstrate 100 can be used, including without limitation an outerdiameter of nominally 96.9 mm to nominally 100.4 mm.

FIG. 2 shows a top plan for a substrate 110 that is also formed of glassand subjected to chemical processing as known in the art, and has anoverall diameter D which in this case is nominally 67 mm. Withoutlimitation, the substrate is designed for recording media to be used inan HDD with a 2½ inch form factor. Other material configurations andprocessing can be used, including substrates of nominally 68 mm. As withthe substrate 100, the substrate 110 is configured for rotation about acenter point 112 and has an interior sidewall 114 at radius 12.5 mm andan outer sidewall 116 at nominally 33.5 mm. As before, other outerdiameters for the substrate 110 can be used including, withoutlimitation, diameters of nominally 66.9 mm to nominally 71.8 mm.

FIG. 3 shows another substrate 120 in accordance with some embodiments.The substrate 120 is shown in a cross-sectional elevational mode. Aspectratios and other relative dimensional aspects may vary. The substrate120 has an inner sidewall 122 at radius R1 and an outer sidewall 123 atradius R2. These values R1 and R2 can correspond to the radii set forthin FIGS. 1-2 above for the 97 mm substrate 100 and the 67 mm substrate110, or can correspond to other values. Chamfered surfaces are depictedat 124, 125, 126 and 127. The chamfered surfaces extend at an angle of45 degrees although other angles can be used as desired, such as but notlimited to 25 degrees. Opposing top and bottom flat surfaces are denotedat 128 and 129.

The substrates 100, 110 and 120 are in an unpolished state and can bemanufactured using known processing techniques apart from thespecialized dimensions and other information disclosed herein. Suchprocessing may include cutting the disc-shaped substrates from planarglass or other material having a thickness substantially correspondingto the final finished thickness of the substrates. Drilling and bevelingoperations may be applied to provide the substrates with the variousfeatures shown in FIG. 3.

FIG. 4 depicts a polished substrate 130 corresponding to the substrates100, 110 and 120 after the application of a polishing process. Thepolished substrate 130 has upper and lower flat surfaces 132, 134, outersidewall 136 (OD surface), and upper and lower relief zones 138, 140.The relief zones 138, 140 are characterized as duboff (DO) zones andprovide a radiused decrease in elevational topography of the substratewith respect to the respective flat surfaces 132, 134. It will beappreciated that the substrate 130 is merely illustrative and differentrelative dimensions of the various depicted aspects can be provided. Thepre-polishing profile is depicted in broken line fashion.

A head is denoted at 142 and may represent a data transducing head(transducer) used once a magnetic recording structure has been formed onthe substrate 130, or may represent a special test head (e.g., a glidehead) used during evaluation of the polished substrate prior to magneticstructure fabrication.

It can be seen that the polishing process generally rounds off the sharpjunctions between the flat surfaces and the outer chamfered surfaces,and erodes the substrate toward the substrate center point. Referencepoint A generally depicts an outer extent of the upper flat surface 132and thus denotes the radial transition point between the flat surface132 and the DO relief zone 138. Point A is sometimes referred to as aradius of rolloff, or ROR point. Reference point B represents a point atwhich the head 142 experiences unstable flight characteristics due tothe negative deviation distance between the flat surface 132 and therelief zone 138 at this point. As noted above, this can vary based on avariety of factors but in some cases may be on the order of about100-200 nm.

Reference point C identifies the maximum deviation distance from the(original) flat surface elevation of the substrate, and thus indicatesthe maximum change in thickness resulting from the polishing process.Reference point D identifies the outermost extent of the recording areaon the finished magnetic recording disc.

It will be appreciated that the various layers of the recordingstructure may be applied to the entirety of the outer surfaces of thesubstrate 130, but the HDD will be configured such that the outermostactive data track is at the radius corresponding to point D. A ramp loadstructure may be placed just outside of point D to facilitate unloadingand loading operations of the head 142.

Point D may be at the same location as point B, or may be radiallyinward of point B as shown. The relative locations and spacings ofpoints A-D can vary depending on a variety of factors including thepolishing process, composition of the substrate, chemical processingapplied to the substrate, test data, product specifications, etc.

In some cases, the distance from the outer sidewall (OD surface) 136 topoint A may be on the order of from about 2.2 mm to about 2.5 mm. Thedistance from the OD surface 136 to point B may be on the order of fromabout 1 mm to about 1.5 mm. The distance from the OD surface 136 topoint C may be on the order of from about 0.2 mm to about 0.5 mm. Thedistance from the OD surface 136 to point D may be on the order of fromabout 1.8 mm to about 2.0 mm. These ranges are merely exemplary andother respective radial distances may be obtained, including distancesthat are greater or smaller than these ranges.

FIG. 5 depicts another example polished substrate 150, which also mayarise from the application of a polishing process to one of theforegoing unpolished substrates 100, 110, 120. The polished substrate150 exhibits a ski jump (SJ) relief zone configuration, characterized asa positive elevation in the relief zone adjacent the OD of thesubstrate. The ski jump profile is generated by displacement of thesubstrate material during the polishing process. In some cases, both DOand SJ characteristics may arise on the same substrate at differentlocations.

The polished substrate 150 includes opposing upper and lower flatsurfaces 152, 154; outer sidewall (OD surface) 156; and upper and lowerski jump (SJ) relief zones 158, 160. As before, point A denotes an outerradial extent of the flat surfaces 152, 154, and therefore connotates aradius of rolloff (ROR) point. Point B denotes the maximum change inelevation over the relief zones 158, 160 at which a head 162 becomesunstable. Point C is the location of the maximum elevation of the reliefzones 158, 160, and point D represents the outermost radial extent ofthe recording area on the finished recording disc. The various distancesfrom the OD surface 156 to points A-D may correspond to the valuesprovided above in FIG. 4, or may be different.

FIG. 6 depicts a standard sized substrate and an enlarged substrate forpurposes of comparison. A 95 mm substrate is represented at 170, and a97 mm substrate is represented at 180. The standard (95 mm) substrate170 includes flat surface 172, DO relief zone 174, chamfer 176 and ODsurface 178. The enlarged (97 mm) substrate 180 similarly includes flatsurface 182, DO relief zone 184, chamfer 186 and OD surface 188. Therespective substrates 170, 180 have nominally the same DO profile. Thesubstrate 180 has an overall radius that is nominally 1 mm larger thanthe substrate 170. Outermost recording areas for the respectivesubstrates are denoted at respective points D.

It can be seen that enlarging the substrate size from 95 mm to 97 mmcould allow for the recording area on the larger substrate to beincreased by a full millimeter in radial extent (or whatever radialdifference exists between the two substrates), thereby increasing theoverall data storage capacity of the resulting 97 mm finished recordingdisc over what was available on the standard sized 95 mm finished disc.

However, in some embodiments a derating factor is used so that less thanall of the newly available real estate is dedicated to the storage ofdata. The derating factor, identified as the value X, has a value offrom 0 to 1 and represents a fraction (or percentage) of the additionalradial extent that is used for the storage of data in the HDD. As shownin FIG. 6, a derating factor of 0.70 (70%) is used so that, for anincrease in radial size of 1 mm, the larger 97 mm substrate provides afinal recording area of an additional 0.70 mm over the 95 mm substrate170. It will be appreciated that if a 99 mm disc is used with a deratingfactor of 0.70, then an additional 1.4 mm of recording space (out of 2.0mm total radial increase) would be used for the storage of data, and soon. The derating factor can be any suitable value as noted above.

While not required, one reason for the use of the derating factor isbased on the recognition that variability in the magnetic discmanufacturing process can result in manufacturing yield losses (scrap)at various stages in the HDD manufacturing process. In some cases, afirst percentage loss X % of product may be lost at the polishingprocess, so that X % of all polished substrates must be scrapped. Asecond percentage loss Y % of product may be lost once the magneticrecording structures have been formed on the viable substrates, such asthrough the use of the aforementioned glide test heads (e.g., 142, 162in FIGS. 6-7). A third percentage loss Z % may be lost after HDDassembly when operational transducers (e.g., 142, 162 in FIGS. 6-7)contact the outer extents of the finished recording discs. Total lossesmay be calculated as (X+Y+Z) %, but it can be seen that the latterlosses, particularly at the HDD product level, can be extremely costly.

Accordingly, by derating the outermost extent of the recording area sothat less than all of the available extra space is not used for therecording of data, it is contemplated that significant cost savings, byway of increased manufacturing yields, can be experienced at each of theabove three manufacturing levels, as well as potentially at othermanufacturing levels as well. For example, process enhancements such asfaster, more aggressive polishing processes, etc. may lead to furthereconomic benefit from the use of the various embodiments set forth inthe present disclosure.

While FIG. 6 depicts 95 mm and 97 mm substrates, it will be appreciatedthat similar benefits can be achieved using 67 mm substrates as comparedto 65 mm substrates, etc.

FIG. 7 is somewhat similar to FIG. 6 in that it depicts 95 mm and 97 mmsubstrates 190, 200 that share a common ski jump (SJ) profile. Asbefore, the 95 mm substrate 190 includes flat surface 192, SJ reliefzone 194, chamfer 196 and OD surface 198. The 97 mm substrate 200includes flat surface 202, SJ relief zone 204, chamfer 206 and ODsurface 208.

The 97 mm substrate 200 has a radius that is nominally 1 mm larger thanthe 95 mm substrate 190. A derating factor of X=0.7 is again used inFIG. 7 so that the recording area of the 97 mm substrate 200 isincreased by 0.7 mm as compared to the 95 mm substrate 190.

FIG. 8 depicts a standard sized substrate and an enlarged substratehaving different DO profiles. As before, the respective substrates arerepresented as a 95 mm substrate 210 and a 97 mm substrate forillustration purposes, but other size substrates can be used as desired.The different DO profiles may arise from a variety of reasons. In someembodiments, a different polishing process is applied to the larger 97mm substrate 220, providing enhanced flatness at the expense of greatermaterial removal at the OD.

The standard sized 95 mm substrate 210 has flat surface 212, DO reliefzone 214, chamfer 216 and OD surface 218; the enlarged 97 mm substrate220 has flat surface 222, DO relief zone 224, chamfer 226 and OD surface228. As before, the 97 mm substrate 220 has a radial extent that isnominally 1 mm larger than the 95 mm substrate 210.

A derating factor of 0.50 is applied so that, in one approach, therecording area of the 97 mm substrate 220 is increased by 0.50 mm.Alternatively, a derating factor of 0 is applied such that bothsubstrates 210, 220 have nominally the exact same recording area. It canbe seen that in this latter case the 97 mm substrate would be expectedto have a significantly better manufacturing yield in the disc and HDDmanufacturing process, as well as exhibiting increased reliability, etc.

FIG. 9 depicts two different substrates with different SJ profiles. A 95mm substrate 230 has flat surface 232, SJ relief zone 234, chamfer 236and OD 238. An enlarged 97 mm substrate 240 has flat surface 242, SJrelief zone 244, chamfer 246 and OD 248. Different polishing is appliedto the respective substrates so that the flat surface 242 of the 97 mmsubstrate is superior to the flat surface 232 of the 95 mm substrate,allowing higher manufacturing yields and performance with regard to therecording structures formed thereon. However, in at least some cases themore effective polishing process (which may take less time) may resultin a significantly greater elevational deviation for the SJ relief zone244 as compared to the SJ relief zone 234.

As before, the recording area for the larger substrate 240 can beincreased, or set to be nominally the same size as the recording areafor the standard sized substrate 230.

FIGS. 10-12 depict aspects of a polishing system 300 that can be used topolish substrates 302 as discussed hereinabove in accordance with someembodiments. The polishing system 300 accommodates the concurrentpolishing of a plurality of the substrates 302 which are inserted intopockets 304 of rotatable carriers 306.

The loaded carriers 306 are sandwiched between opposing upper and lowerpads 308, 310, which rotate in opposing directions as generally depictedin FIG. 12. Inner and outer tracking mechanisms, such as gear teeth,spaced apart pins, etc. are provided at 312, 314 in FIG. 10. Thus, asthe pads 308, 310 rotate about a main central point 316, the carriers306 also rotate around respective central points 318 of each carrier(FIG. 11). This provides a kinematic sweep, or circuitous path, for eachsubstrate 302 as it passes through a full rotation around the centerpoint 316.

As shown in FIG. 11, each of the pockets 304 have a center point that isaligned at a selected radius 320 of the carrier 306. This selectedradius 320 is sometimes referred to herein as a “bolt circle.”

The pads 308, 310 may have various characteristics such as stiffness(compressibility), form, abrasiveness, etc. A slurry of abrasives andother materials may be introduced to facilitate the polishing process.As noted above, more aggressive polishing approaches can be taken sinceit is less important that the outermost portions of the substrates bemaintained within specified tolerances to achieve the desired outermostrecording area characteristics.

In some embodiments, a method and formula can be provided to optimizethe kinematic sweep of the substrates 302 irrespective of tool type(e.g., polisher's gear radius, plate size, etc.) so as to keep thepockets 304 at a safe distance from the edges of the pads 308, 310 toprevent damage from scratches while optimizing kinematic sweep. Theformula and method generally include calculating a gap distance from padto gear and then calculating the distance from the edges of the pads308, 310 to the bolt circle 320. It will be appreciated that, duringpolishing, all portions of the substrates 302 should remain within theinner and outer edges of the pads 308, 310 (e.g., the carrier pockets304 have to be fully over/under the pads 308, 310).

There are at least two issues associated with current methods forlocating the pockets on a carrier (that is, calculating the size andlocation of the bolt circle 320).

The first issue is not taking the pad area into consideration. If theoutside of the pocket 304 is free to travel beyond the edge of the pad(pad diameter), the part being polished is able to pick up debris thatcollects at the edges of the pads 308, 310. This increases the chancesof dragging foreign debris or particles back onto the pads as the partcontinues to rotate inwards and becomes an obvious source of scratchdefect on the parts being polished.

Being aware of the first problem means that one should design thecarrier 306 (including the bolt circle 320) with how it relates to thepads 308, 310. This usually means either making a rough estimate, byputting the carrier on the machine and measuring, or using a CAD systemto see the relationship. This is time consuming and subject to erDO.Moreover, this becomes even more difficult if different OD sizes ofsubstrates are used, as disclosed herein.

The following formula can be used to calculate the bolt circle diameter,regardless of machine type, disc pocket size, or carrier size:

$\begin{matrix}{{BC} = {C - \left\lbrack {\left( {\frac{O\; G}{2} - \frac{P}{2}} \right) + \frac{C\; P}{2} + K} \right\rbrack}} & (1)\end{matrix}$where BC is the bolt circle diameter (in millimeters, mm), C is thecarrier diameter, OG is the outer gear diameter, P is the pad diameter,CP is the carrier pocket diameter, and K is a derating constant thatcontrols the amount of distance from the edge of the pocket to the edgeof the pad. A suitable value for K may be 10, or some other value.

In some embodiments, being less concerned about the location of the RORpoint and the topography of the substrate beyond the ROR point can allowuse of a more compressible pad, which may facilitate the use of aslightly larger particle size. In one example where an abrasive particlesize (d50) of about 0.6-0.8 micrometer, μm (d50) and a relatively harderpad were required to meet certain polishing criteria for a set ofsubstrates, it was found that a larger abrasive particle size of about0.8-1.0 μm particle size with a softer pad could be safely used. Thelarger particle size generally increased removal rate of the material(“stock removal rate”), and the use of a softer pad absorbed thepressure from the larger partices in the distribution. As a result,sub-surface damage from the polishing process was found to be similar tousing the original (0.6-0.8 μm) sized partice/harder pad combination.

Using the same particle size, but increasing pressure, would also tendto increase the stock removal rate. Again, if there is less emphasis onthe location of the roll off radius point, higher pressure could be usedto expedite the process and obtain improved polishing characteristics.

Polish slurries are formulated with edge condition (roll off radius) inmind. Less emphasis on roll off radius would allow slurry suppliers morefreedom to formulate their slurries to provide optimum results for therecording portions of the finished discs.

FIG. 13 is a schematic representation of a finished magnetic recordingdisc (medium) 330 in accordance with some embodiments. Otherconfigurations can be used. Generally, the medium 330 includes a basesubstrate 332, a soft underlayer (SUL) 334, an interlayer 336, one ormore recording layers 338, a protective carbon overcoat (COC) layer 340and an optional lubricant layer 342. The various thicknesses of therespective layers can vary, and the substrate may be significantlythicker than the remaining layers.

The layers 334-342 form a magnetic recording structure. The magneticrecording structure can be adapted for use in a variety of operationalrecording environments, including but not limited to longitudinalrecording, perpendicular recording, heat assisted magnetic recording(HAMR), bit patterned media, printed media, self-organizing media, CGCmedia, etc. It is contemplated that better magnetic data recording andread performance over the radial extent of the substrate can be obtaineddue to better flatness characteristics of the substrate.

The substrate 332 is contemplated as comprising an enlarged substrate asdiscussed above, such as but not limited to a substrate of OD dimensionsof nominally about 96.9 mm up to about 100.4 mm for 3½ inch form factordrives, and nominally from about 66.9 mm up to about 71.8 mm for 2½ inchform factor drives.

FIG. 14 is a simplified representation of standard sized hard disc drive(HDD) 400 with magnetic recording media having an enlarged outerdiameter. In the case of a 3½ inch form factor, the HDD 400 has outerlength and width dimensions of nominally 146.1 mm by 101 mm. In the caseof a 2½ inch form factor, the HDD has outer length and width dimensionsof nominally 101 mm by 73 mm Media of 97 mm or 67 mm, or other sizeslarger than the standard 95 mm or 65 mm sizes, may be used as discussedabove.

The HDD 400 includes a head disc assembly (HDA) 402 housed within a basedeck 404. A top cover 406 is mated to the base deck 404 to provide anenvironmentally controlled interior environment for the HDD 400.

A spindle motor 408 is mounted to the base deck 404 to rotate a stack ofmagnetic recording media (discs) 410, in this case two, at a constanthigh speed such as 10,000 revolutions per minute (rpm). Data read/writetransducing heads (transducers) 412 are controllably advanced acrossrecording surfaces of the media 410 by way of a rotatable actuator 414and a voice coil motor (VCM) 416.

A load/unload ramp structure 418 is positioned adjacent an outermostdiameter of the media 410 to receive the transducers 412 when the HDD isdeactivated. A flex circuit 420 provides control signals between thetransducers 412 and HDD electronics on an externally mounted printedcircuit board assembly (PCBA) 422.

A standard form factor configuration drive may require some internalmodifications to accommodate a larger media size as described herein.The position and extent of the ramp structure 418, for example, mayrequire adjustment to accommodate the larger discs/substrates.Similarly, outer shroud surfaces may require adjustment outwardly toaccommodate the extra required clearance for the enlargeddiscs/substrates. It is contemplated that there is sufficient roomwithin the confines of a 3½ inch form factor drive to accommodate discsof up to about 100.4 mm in diameter, and there is sufficient room withinthe confines of a 2½ inch form factor drive to accommodate discs of upto about 71.8 mm in diameter. Other sizes can be used as well.

FIG. 15 illustrates a portion of another standard sized HDD 430, whichfor purposes of illustration is contemplated as a 3½ inch form factor.Other sizes can be used such as the 2½ inch form factor. The HDD 430includes a base deck 431 similar to the base deck 404 shown in FIG. 14and has a substantially vertically extending sidewall 432. One or morerotatable magnetic recording discs 434 (in this case, two) are axiallyaligned for rotation within the interior confines of the base deck 431.The base deck 431 can be formed using any number of suitable processesincluding casting with secondary machining, injection molding, etc.

An interior shroud structure 436 is formed as a portion of the base deck431. The shroud structure 436 includes an inner curvilinearly extendingshroud surface 438 which extends in close proximity to the outermostedge of the discs 434. The shroud structure 436 is integral with thebase deck sidewall 432. In the embodiment of FIG. 15, the base decksidewall 432 has a nominal thickness T, such as but not limited to about0.2 mm, and a portion of the sidewall 432 includes a circumferentiallyextending shroud surface 439 that coextends with the shroud surface 438to provide continuously curvilinear shrouding for the discs 434.

In this case, the minimum sidewall thickness T, and the minimumshrouding distance S (being the distance between the discs 434 and theshroud surfaces 438, 439) help to define the maximum outermost diameterof the discs 434. For example, in a 3½ inch form factor disc, the widthis nominally 101 mm, and if T=0.2 mm and S=0.1 mm then a maximum discdiameter D can be given by:D=101−2(T)(S)=101−2(0.2)(0.1)=101−2(0.3)=101−0.60=100.4 mm  (2)

Accordingly, an outer diameter of 100.4 mm can be used with a base decksidewall width of nominally 0.2 mm and a shroud surface clearance ofnominally 0.1 mm. Similarly, for a 2½ diameter form factor having awidth of nominally 73 mm, a largest outer diameter for the discs can be71.8 mm using a sidewall width of 0.2 mm and a shroud surface clearanceof 0.1 mm.

FIG. 16 depicts another hard disc drive (HDD) 440 similar to the HDD 430in FIG. 15. The HDD 440 is also contemplated as a standard sized formfactor HDD, such as the 3½ inch form factor. The HDD 440 includes a basedeck 441 with vertical sidewall 442, disc(s) 444, shroud structure 446and interior shroud surface 448.

To enable further expansion of the size of the discs 444, the sidewall442 is provided with a through-hole aperture 450, as shown in FIG. 17.The aperture 450 can take any suitable shape including round, square,elongated, curvilinear, etc. The sidewall thickness can taper as shownat 451 in a direction toward the aperture 450.

A sealing member 452 can thereafter be applied to the sidewall 442 tosealingly cover the aperture 450, as depicted in FIG. 18. The sealingmember can be a relatively thin material such as metal or plastic film.A layer of adhesive or other bonding agent (not separately shown) can beused to affix the sealing member 452 to the sidewall 442. The sealingmember 452 thus constitutes a thinner section of the sidewall 442.

It can be seen from FIG. 16 that the use of a clearance aperture 450 anda sealing member 452 allows for further clearance reductions andcorresponding increases in disc diameter. For example, if the minimumclearance distance C between the outermost edge of the discs 444 and theinterior surface of the sealing member 452 is nominally equal to S (e.g.S=C=0.1 mm), then a maximum diameter of the disc D in a 3½ inch formfactor is given by:D=101−2(C)=101−2(0.1)=101−0.2=100.8 mm  (3)

Accordingly, discs with diameters as large as about 100.8 mm may be usedin 3½ inch form factor drives with the aperture and sealing memberarrangement of FIGS. 16-18. Similarly, discs with diameters as large asabout 72.8 mm may be used in 2½ inch form factor drives with theaperture and sealing member arrangement of FIGS. 16-18.

FIG. 19 is a schematic depiction of another data storage device 500 inaccordance with some embodiments. The data storage device 500(hereinafter hard disc drive, HDD) is characterized as a standard-sizedHDD such as a 3½ inch form factor HDD or 2½ inch form factor HDD. Theschematic depiction of FIG. 19 is representational in nature and is notdrawn to scale nor is it provided with accurate aspect ratios, profiles,etc.

The HDD 500 includes a housing 502 formed from a lower HDD housingmember (“base plate”) 504 and an upper HDD housing member (“cover”) 506.The base plate 504 and cover 506 cooperate to form a sealed interiorenvironment within the housing 502.

The base plate 504 has a base portion 508 which is a substantiallyplanar member that extends normal to and in a spaced-apart relation witha magnetic recording disc 510. The magnetic recording disc 510 uses anenlarged substrate as discussed above, and may have various features asdescribed above such as a planar portion, a duboff (DO) region, a skijump (SJ) region, etc.

The magnetic recording disc 510 is arranged for rotation about a centralaxis 512 using a spindle motor 514. The motor 514 has a stationaryportion (stator) 516 mounted within a boss 517 of the base portion 508and a rotatable hub (rotor) 518 which supports the magnetic recordingdisc 510. The disc 510 is secured to the hub 518 using a lower shouldermember 520 and an upper clamp 522. While a single disc 510 is shown, itwill be appreciated that multiple axially aligned discs can be providedwith intervening spacers or other support members. An actuator assembly(not shown) supports a number of data transducers adjacent the upper andlower recording surfaces of the disc 510.

Distances A, B and C are shown in FIG. 19. These distances are measuredfrom the central axis 512. The first distance A represents an averageoverall distance from the central axis 512 to an outermostcircumferential edge 524 of the disc 510. An average overall distance isused since there may be a relatively small axial offset of the disc 510relative to the hub 518. Nevertheless, the average overall distance willcorrelate to the overall diameter of the disc 510.

The second distance B represents an overall distance from the centralaxis 512 to an interior surface 526 of a sidewall portion 528 of thebase plate 504. The interior surface 526 is in facing relation to theoutermost edge 524 of the disc 510 and at a common elevation as thedisc, as shown. The difference D between the distances A and B (D=B−A)corresponds to the average outermost clearance between the disc 510 andthe base plate 504. As noted above, it is contemplated that thisclearance distance D will tend to be smaller than what is normallyachieved in conventional HDDs with standard sized media.

The third distance C in FIG. 19 represents an overall distance from thecentral axis 512 to an exterior surface 530 of the sidewall portion 528.For clarity, the view in FIG. 19 is contemplated as displaying thenarrower width dimension of the device; that is, FIG. 19 provides a span(side-to-side outer distance between opposing sidewalls 528) ofnominally 101 mm for a 3½ inch form factor drive and a span of nominally73 mm for a 2½ inch form factor drive. While not necessarily limiting,it is contemplated that the central axis 512 will be nominally centeredover this span.

Exemplary values for the distances A, B and C in FIG. 19 are set forthby Table 1.

TABLE 1 HDD Size A B C 3½ inch form At least 48.5 mm 50 mm or less 50.5mm factor HDD 2½ inch form At least 33.5 mm 36 mm or less 36.5 mm factorHDD

Other values can be used for the distance values A and B. The distancevalue C is largely fixed assuming a centered medium within the housing.It can be seen that using enlarged substrates as disclosed hereinreduces the available budget for outer disc clearance (e.g., thedistance D=B−A) between the discs 510 and the sidewall surfaces 526 ofthe HDD housing. Using a thinner sidewall 528 can enable the use of alarger substrate while still maintaining a given disc/sidewall clearancedistance.

FIG. 20 provides another option to facilitate the use of enlargedsubstrates, namely, the use of clearance channels (apertures) asdescribed above in FIGS. 16-18. FIG. 20 shows a second HDD data storagedevice 540 substantially identical to the HDD 500 of FIG. 19, except asnoted below. For ease of discussion, like reference numerals are used todenote similar components in FIGS. 19-20.

The opposing sidewalls 528 of FIG. 20 each include a clearance channel542 which extends into the interior surface 526 of the sidewall asshown. The clearance channel 542 may extend partially into the sidewallor may extend all the way through the sidewall from the interior surface526 to the exterior surface 530, in which case a cover member may beused to cover and sealingly span the clearance channel as depicted inFIG. 18. It will be appreciated that the sidewalls 528 have a nominalthickness and the clearance apertures 542 provide a localized reductionin thickness of the sidewalls.

The same general values for the respective distances A, B and C fromTable 1 can be applied to the configuration of FIG. 20. The clearancechannels 542 can further serve as disc deflection limiters to limit discdeflection responsive to mechanical shock events.

FIG. 21 is an illustrative format for data tracks that may be formed onmagnetic recording discs having enlarged substrates as disclosed herein.A data track 550 includes a number of spaced apart servo fields 552. Theservo fields 552 store various types of servo control information usedto control the position of data read/write transducers adjacent themedia recording surfaces. The servo control data can include servosynchronization (sync) data, automatic gain control (AGC) data, index(angular position) data, Gray code (radial position) data, servo bursts(for intra-track position detection and control), RRO compensationvalues, etc.

The servo fields 552 may radially extend from the innermost diameter(ID) to the outermost diameter (OD) of the medium, much like spokes on awheel. The servo fields may be written at a constant frequency or may bewritten at different frequencies at different radial locations.

User data sectors 554 are defined in the spaces along the tracks 550between adjacent pairs of the servo fields 552. The number of datasectors 554 between any adjacent pair of servo fields can vary based ona number of factors such as radius, disc size, number of servo fields,data capacity of the data sectors, etc. In some cases, split sectors maybe used so that a first portion of a sector appears before a given servofield 552 and a remaining second portion of the sector appears after thegiven servo field 552. Each data sector 554 may have a predeterminedfixed size and may store a selected amount of user data, such as 512bytes, etc.

It will be appreciated that the various embodiments disclosed hereinallow the placement of data tracks such as 550 at locationssignificantly farther from the center of the discs as compared to mediaformed using standard sized substrates. For example, in a 3½ inch formfactor HDD an outermost data track 550 arranged as shown in FIG. 21 canbe at an average radius greater than 47.5 mm from the center ofrotation. In a 2½ inch form factor HDD, an outermost track such as 550can be at an average radius greater than 32.5 mm from the center ofrotation. Such tracks can represent the most valuable real estate on thediscs due to the greater linear velocity (and hence, higher potentialfrequency) as well as proximity to load/unload ramps or otherstructures. Using enlarged substrates thus provide enhanced performancecapabilities in this area as well.

It will now be appreciated that the various embodiments of the presentdisclosure can provide a number of benefits. By enlarging the size of asubstrate for a magnetic recording disc from the standard sizes of 95 mmand 65 mm, enhanced data recording and read characteristics can beachieved over the entirety of the radial distance of a recording area ofthe discs formed from such substrates. Enhanced performance at theoutermost extents of the recording media can be obtained. The use of aderating factor allows for the same, or better, overall data storagecapacity to be attained while improving manufacturing yields, processtimes, etc.

For purposes of the appended claims, a 3½ inch form factor hard discdrive (HDD) will be defined consistent with the foregoing discussion tohave length and width dimensions of nominally 146.1 mm by 101 mm andsized such that two 3½ inch form factor HDDs in a side-by-sidearrangement have a corresponding footprint of a 5¼ inch form factor HDD.A 2½ inch form factor HDD will be defined consistent with the foregoingdiscussion to have length and width dimensions of nominally 101 mm by 73mm and sized such that two 2½ inch form factor HDDs in a side-by-sidearrangement have a corresponding footprint of a 3½ inch form factor HDD.

It is to be understood that even though numerous characteristics andadvantages of various embodiments of the present disclosure have beenset forth in the foregoing description, together with details of thestructure and function of various embodiments, this detailed descriptionis illustrative only, and changes may be made in detail, especially inmatters of structure and arrangements of parts within the principles ofthe present disclosure to the full extent indicated by the broad generalmeaning of the terms in which the appended claims are expressed.

What is claimed is:
 1. A data storage device comprising: a housingmember for a 3½ inch form factor storage device; a data recording discsupported by the housing member and having an overall diameter ofnominally from 96.6 mm to 100.8 millimeters, mm; and a data read/writetransducer configured to be controllably advanced across a recordingsurface of the data recording disc and to record data to data tracksadjacent an outermost perimeter of the data recording disc beyond anominal radius of 47.5 mm from a center of rotation of the datarecording disc.
 2. The data storage device of claim 1, wherein thehousing member is a base deck of the 3½ inch form factor storage devicehaving nominal dimensions of 146.1 mm by 101 mm.
 3. The data storagedevice of claim 1, wherein the overall diameter of the data recordingdisc is nominally from 96.9 mm to 100.8 mm.
 4. The data storage deviceof claim 1, wherein the overall diameter of the data recording disc isnominally 97 mm, 98 mm, 99 mm or 100 mm.
 5. The data storage device ofclaim 1, further comprising storage device electronics supported on anexterior printed circuit board (PCB) affixed to the housing memberopposite the data recording disc, the storage device electronics inelectrical communication with the data read/write transducer.
 6. Thedata storage device of claim 1, further comprising a spindle motorsupported by the housing member, the spindle motor supporting the datarecording disc and configured to rotate the data recording disc at aselected rotational velocity.
 7. The data storage device of claim 1,further comprising a load/unload ramp structure supported by the housingmember at a position adjacent the outermost perimeter of the datastorage device to facilitate contacting support of the transducer awayfrom the data recording surface responsive to transitioning of the datastorage device to a deactivated state.
 8. The data storage device ofclaim 1, further comprising a rotary actuator which supports thetransducer and pivots about a pivot point adjacent the outermostperimeter of the data storage device responsive to an application ofcurrent to a voice coil motor (VCM).
 9. The data storage device of claim1, wherein the housing member is characterized as a base deck, the datastorage device further comprising a top cover which mates with the basedeck to form a sealed enclosure in which the data recording disc and thedata read/write transducer are disposed.
 10. A data storage devicecomprising: a housing member for a 2½ inch form factor storage device; adata recording disc supported by the housing member and having anoverall diameter of nominally from 66.6 mm to 71.8 millimeters, mm; anda data read/write transducer configured to be controllably advancedacross a recording surface of the data recording disc and to record datato data tracks adjacent an outermost perimeter of the data recordingdisc beyond a nominal radius of 32.5 mm from a center of rotation of thedata recording disc.
 11. The data storage device of claim 10, whereinthe housing member is a base deck of the 2½ inch form factor storagedevice having nominal length and width dimensions of 101 mm by 73 mm.12. The data storage device of claim 10, wherein the overall diameter ofthe data recording disc is nominally from 66.9 mm to 71.8 mm.
 13. Thedata storage device of claim 10, wherein the overall diameter of thedata recording disc is nominally 67 mm, 68 mm, 69 mm or 70 mm.
 14. Thedata storage device of claim 10, further comprising storage deviceelectronics supported on an exterior printed circuit board (PCB) affixedto the housing member opposite the data recording disc, the storagedevice electronics in electrical communication with the data read/writetransducer.
 15. The data storage device of claim 10, further comprisinga spindle motor supported by the housing member, the spindle motorsupporting the data recording disc and configured to rotate the datarecording disc at a selected rotational velocity.
 16. The data storagedevice of claim 10, further comprising a load/unload ramp structuresupported by the housing member at a position adjacent the outermostperimeter of the data storage device to facilitate contacting support ofthe transducer away from the data recording surface responsive totransitioning of the data storage device to a deactivated state.
 17. Thedata storage device of claim 10, further comprising a rotary actuatorwhich supports the transducer and pivots about a pivot point adjacentthe outermost perimeter of the data storage device responsive to anapplication of current to a voice coil motor (VCM).
 18. The data storagedevice of claim 10, wherein the housing member is characterized as abase deck, the data storage device further comprising a top cover whichmates with the base deck to form a sealed enclosure in which the datarecording disc and the data read/write transducer are disposed.
 19. Adata storage device comprising: a base deck for a 2½ inch form factorstorage device, the base deck having nominal length and width dimensionsof about 101 mm by 73 mm; a disc stack assembly supported by the basedeck comprising a rotatable spindle motor hub which contactinglysupports a plurality of axially aligned data recording discs each havingan overall diameter of nominally from 66.6 mm to 71.8 millimeters, mm;and a rotary actuator which supports a corresponding array of dataread/write transducers each configured to be controllably advancedacross a respective recording surface of the data recording discs and torecord data to data tracks adjacent an outermost perimeter of the datarecording discs beyond a nominal radius of 32.5 mm from a center ofrotation of the disc stack assembly.
 20. The data storage device ofclaim 19, wherein at least one recording surface of the data recordingdiscs extends at a nominal radius of at least 33.3 mm from the center ofrotation of the disc stack assembly.